Indiana Gov. Mike Pence has fired a shot across the bow with an open letter to President Obama warning that if the new rule is not improved “Indiana will not comply.”

Pence’s declaration echoes a growing theme among governors and attorneys general who have in recent months made similar declarations regarding an over-reaching federal government which they argue poses direct usurpation of 10th Amendment rights.

Should Indiana follow through with nullification of the EPA’s rules, other states are likely to take the cue and refuse enforcement.